To build a drip irrigation system for raised beds, I connected a polyethylene tube (carrying water to the plant beds) to soaker hose (used on the beds themselves). The PE tubing is 0.6 inches inside diameter, while the soaker hose is 3/8 inches in diameter. So far, my solution for connecting the two was to use the following the adapter shown below on the end of the PE tubing and screwing the threaded end of it into one of the fittings that came with the soaker hose, but this arrangement tends to leak heavily. Is there a better way of connecting the hose to the tubing? Below are the pictures of the soaker hose, the PE tubing, the soaker hose fitting, and the adapter for the PE tubing that I have worked with:
Consider getting a metal juncture.
I hate to throw out a good hose just because the metal threads got run over. Here is the old hose and "new" brass thread replacement. The hose is held on with a pipe clamp which is the silver piece - you put it around and tighten it up with a screwdriver. You will see that red rubber I put under the hose clamp. I was worried the old hose was thin and brittle and would not have enough purchase on the new metal and then when there was pressure it would leak around or just blow off the pistol attachment. I have been very pleased with the red rubber addition to the pipe clamp hose fix and wish I had thought of it years ago. Or maybe it would have been fine with just the pipe clamp and old hose. Historically not.
Cut a piece of soak hose and a piece of your PE tube and go to the hardware store. Find a piece of metal (or two pieces) that join them well. The metal should extend on the inside of the hose. Get a couple of pipe clamps to hold the metal on good to your hoses. The pipe clamp is supposed to squeeze the (relatively) soft hose against the hard piece underneath and inside. You can do the red rubber part too if you are inclined, or use some scrap rubber you have handy. The red rubber I used was actually left over from a previous attempt to cut a gasket.
I know you already own a bunch of plastic hose parts. I get frustrated with plastic plumbing parts but it is a shame not to try to get use out of them. Maybe you can make them seal better against the pressure with the hose clamp and rubber like I used here with the metal threads? You could try that first before you buy any brass and that is what @crip659 suggested in the comment up there.